One of the most important changes to occur in computers during the last decade was the shift from character-based to graphic-based software. Character-based software requires a user to input one or (usually) more keystrokes on a conventional typewriter keyboard in order to execute commands. The "Macintosh" computer from Apple was the first commercially successful computer to allow the user to execute commands without using the keyboard. The Macintosh was supplied with a cursor control device, or "mouse," that translated complex motions of the mouse in two dimensions relative to the surface upon which it was moved into corresponding movements of a cursor or other icon on the monitor screen or other display device of the computer. Software designed to take advantage of the mouse-style controller allows a computer user to draw shapes by translating the movement of the mouse into movements of a "pen" or "brush" on the screen, or to choose files or commands represented by icons, "buttons," or other images on the screen by moving the mouse until the cursor is aligned with the desired file or command icon and then selecting it by "clicking" a switch located on the mouse.
The mouse itself generally consists of (1) a housing shaped to fit comfortably under the user's hand, (2) one or more buttons located on one or more surfaces of the mouse controlling dual-position switches, and (3) a mechanism used to control the on-screen movement of the icon, which generally consists of a ball of high specific gravity held within a cavity in the housing so that a small portion of the ball protrudes beyond the housing. The ball is coated with a substance with a high coefficient of friction and is held loosely within the cavity so that, for example, the ball rotates freely within the housing when the housing is moved relative to a flat horizontal surface composed of a compatible material. In a typical configuration, two generally cylindrical shafts attached to electromechanical transducers press against the ball so that the rotation of the ball is converted in to rotation of one or both of the shafts. Rotation of each such shaft creates a control signal that is supplied to the computer. The cylindrical shafts are oriented within a single plane and at a relative angle of 90.degree. so that movement of the mouse is translated into cursor or arrow movement along both X and Y coordinates on the computer screen.
The scale used by the computer to translate movement of the mouse into movement on the screen is determined by software and is generally adjustable by the user. With high sensitivity settings, small movements of the mouse produce relatively large movements on the screen. With low sensitivity settings, relatively larger movements of the mouse are required to produce a given amount of screen movement. High sensitivity settings allow small hand movements to move the cursor across the entire screen, but make precise gestures difficult. Users therefore often choose lower sensitivity settings that allow greater precision at the cost of requiring larger hand movements and a larger surface area upon which to operate the mouse.
The requirements for large hand movements and relatively large amounts of desk or other surface area upon which to move the mouse are significant drawbacks in many applications. Another ergonomic shortcoming of the mouse is inherent in its operating principle. Because the mouse produces control signals only when the entire mouse moves, the location of the mouse constantly changes, and the user must "find" the mouse each time it is used. In applications that require only occasional use of the mouse, such as word processing and spreadsheets, the cumulative effect of the many small delays this causes can become an annoyance. A mouse is also difficult to use as a "pen" or "paintbrush:" the point of the pen, or the point around which movement of the mouse generates signals, is in effect the center of the ball, which is totally hidden from view by the ball and the body of the mouse. This greatly limits the value of a mouse in graphics and engineering applications.
A variation of this style of mouse, one that addresses some but not all of its shortcomings, is the trackball. The trackball is essentially an inverted mouse. The housing is stationary, and the ball protrudes from the top of the housing. The user creates control signals by directly manipulating the ball. As with a mouse, the sensitivity of the screen image to the movements of the ball is generally adjustable.
Because it is stationary, the trackball allows the computer user to work in a smaller space than a mouse. Trackballs are now built into the keyboards of many desktop and a few laptop computers. However, the trackball has a number of limitations as a precision controller. The mouse and the trackball are essentially equivalent in precision and ease of use for small "point-and-select" movements: each allows easy fingertip control. But when a mouse and a trackball are both calibrated for high precision, so that relatively large movements of the internal ball are required for large on-screen movement, a trackball becomes relatively inefficient and awkward. With a mouse, such movements can be accomplished with a single continuous movement of the mouse, albeit a large and space-consuming one. With a trackball, such motions are impossible. Large screen motions are likely to require a user to repeatedly lift his or her hand from the ball and stroke across the ball. Such motions are both imprecise and inefficient, particularly in graphics and engineering applications.
The degree to which such problems affect a given trackball are largely determined by the size of the ball. Currently available trackballs range in size from approximately two inches in diameter, for the largest desktop models, to approximately one-half inch for the smallest trackballs, which are designed to be attached to laptop computers. Larger trackballs allow greater precision because a larger hand movement is translated into the same movement of the ball in terms of degrees of angular movement. However, even the largest available trackballs are not well-suited to use in graphics and engineering applications because (a) large continuous gestures are impossible and (b) a stationary ball is difficult to use for precision drawing and cannot be used for tracing, both of which are essential in engineering and graphics applications.
The third major type of pointing device is the graphics tablet. These devices are marketed by a number of suppliers, including, for example, Summasketch. Unlike the mouse and the trackball, the graphics tablet is not a mechanical device. The graphics tablet consists of a flat surface containing, for example, a gridwork of wires and a pointing device containing an electric coil. The electric grid senses the electrical field generated by the coil and produces control signals that are converted by the computer into X and Y axis coordinates. The coil in the pointing device is generally imbedded in clear plastic so that the user can see the spot the device is pointing at underneath the center of the coil. Graphics tablets are thus well-suited for tasks such as tracing. The graphics tablet is superior to the mouse and the trackball for drawing and engineering applications for this reason. However, the graphics tablet is significantly more expensive than the mouse and trackball, and requires that the user devote table or desk space to a bulky pad. The maximum hand movement and the largest traceable drawing are also determined by the size of the tablet.
The choice between existing products is thus based upon a number of tradeoffs. A mouse allows relatively high precision but requires considerable desk space, and is limited by the fact that the point of the mouse is obscured by the ball and the body of the mouse. Trackballs require less space than mice, but are less precise for large gestures, particularly if the ball itself is small, and are poorly suited to engineering and drafting applications. Graphics tablets are well suited to such tasks, but are too expensive and bulky for most users. Thus, none of the existing pointing devices is entirely satisfactory.
Ideally, a cursor control or pointing device could be used as either a mouse or a trackball depending upon the software application or the preferences of the user. When used as a trackball, it should give the precision of a large trackball while sharing the small footprint of a small trackball. A pointing device should be ergonomically designed, so that it is comfortable to hold and use. Finally, a pointing device should be suitable for drawing and tracing.
These and other objects of the present invention will be apparent to those skilled in the field from the following detailed description of a preferred embodiment.